1. Field of the Invention
The present invention relates to manual transmissions for automotive use able to produce multiple forward drive ratios, the number of the ratios being determined by the configuration of the gear arrangement. More particularly, this invention pertains to a manual automotive transmission in which reverse drive is produced by an endless, flexible chain or belt that transmits power between an output shaft and a countershaft without the use of a reverse idler gear and its associated shift mechanism.
2. Description of the Prior Art
Transmissions that provide five forward speed ratios and a reverse drive ratio generally have three cross-over positions for the shift selector shaft. Each cross-over position selects an appropriate shift fork, which may be moved in opposite longitudinal directions to engage two gear ratios. The first cross-over position selects the first and second forward speed ratios, the second selects the third and fourth speed ratios and the third selects the fifth forward and reverse speed ratios. The presence of the fifth forward speed ratio requires that the countershaft be extended in length from that required in transmissions having only four forward drive ratios in order to carry the additional fifth speed pinion and often the fifth speed synchronizer clutch as well. U.S. Pat. Nos. 4,337,675 and 4,228,693 describe examples of five speed ratio manual transmissions that require longer countershafts than that required for the four forward speed version of the transmissions. Similarly, the output shafts for the transmissions disclosed in these patents require means to fix the fifth speed output gear and the fifth speed synchronizer clutch on the output shaft. U.S. Pat. No. 4,222,281 describes a four-speed ratio transmission whose countershaft has been extended and whose shift mechanism has been modified to accommodate the five speed ratio form of the transmission disclosed in U.S. Pat. No. 4,307,624.
Manual transmissions generally require a reverse idler gear that is moved along the axis of its supporting shaft into meshing engagement with a reverse drive pinion and a reverse output gear through the action of the shift mechanism whose motion is controlled by the vehicle operator. Generally reverse drive is produced by a shift mechanism which includes a reverse motion bell crank that transmits shifting motion of a shift selector shaft to the reverse idler in a direction that is opposite from that applied to the shift selector shaft. This reverse motion mechanism is required in order to maintain the conventional shifting pattern through which the shift selector shaft is moved where the reverse idler must be moved in a direction opposite to that produced by the standard direction of the gear selector. Where the reverse motion mechanism and reverse idler gear are required, the transmission casing must have an enlarged space to accommodate the additional parts required, particularly for the reverse idler and its supporting shaft. The reverse shift mechanism of this type requires necessarily a greater number of parts than would be required if the reverse idler were absent or if the reverse motion mechanism were not necessary. Furthermore, if the need to move the reverse idler on its supporting shaft were eliminated, the number of shift mechanism parts, the complexity of the mechanism, the weight and the overall cost would be appreciably less than that of conventional transmissions.